Mineral oil stocks are a prime source of lubricants for an almost endless list of applications. Lubricating oils and related hydraulic and transmission fluids for present day machinery, internal-combustion engines, and other uses, contain a wide variety of additives.
Increased engine operating temperatures and increased complexity of antipollution devices associated with such engines have resulted in substantial increases in additive quantities in automotive lubricating oils. The quantities of additives employed for improved properties in some instances have been approaching quantities so large as to affect negatively the primary mission of the lubricating oil: to lubricate.
Many materials have been prepared for use in lube oils as viscosity index improvers, such as described in U.S. Pat. No. 3,554,911, U.S. Pat. No. 3,630,905, and British Pat. No. 1,567,654. U.S. Pat. No. 3,994,815 summarizes some of the various hydrogenated arene/conjugated diene copolymers used in lubricating oils as viscosity index improvers.
Needed are polymeric products which are temperature stable, substantially non-degradable by oxygen/temperature, and capable of producing a high level of thickening power in oil at much lower dosage levels than heretofore feasible. With increased costs of base petroleum stocks, it is necessary to find ways to improve thickening powers of viscosity index improvers, to hold down amounts thereof required, and thus hold down costs of the lubricating oils to the American motorist.